Standardization of Threads for Fire Hose Couplings and Fittings

Report of National Board of Fire Underwriters Committee on Fire Prevention and Engineering Standards

FAILURE to recognize that the subject of Standardization of Fire Hose Threads was of countrywide magnitude and importance, has resulted in localized activities securing the adoption and use of a great variety of differing threads. Experience gained in combating large spreading fires indicates that in a great many instances the variations in diameter or pitch of threads are such that those in service in nearby municipalities called upon to render aid could not be connected up with those of the afflicted city or town. Enormous fire losses, constituting a serious drain upon American efficiency, have been due in no small measure to this lack of uniformity in fire hose threads.

Confusion due to misfits experienced in the great Boston fire of 1872 was followed by the general adoption in that section of the country of the so-called Roxbury thread, having an outside diameter of 3-1/16 inches and a pitch of 7 threads to the inch. New York City happened to adopt a thread with 3 inches outside diameter and 8 threads to the inch, which has become a local standard through general adoption in most of the New Jersey and New York state municipalities within a radius of 50 to 75 miles of the metropolis. Years ago the cities and towns of the extreme west, following the precedent set by San Francisco, adopted what was known as the Pacific Coast Standard, a thread with a 3 inch outside diameter and 7 1/2 pitch. Some fairly large cities adopted a pitch of 6 threads to the inch, on the theory that it was less subject to mechanical injury and required fewer turns in connecting up. Enterprising manufacturers induced a considerable number of municipalities to equip themselves with some of the various types of snap or clutch couplings.

These local standards have been adopted in most instances over considerable areas, thereby creating a more or less general feeling of sectional security and complacency. Experience has shown that such a feeling is not justified, as there are too many cases where the threads of nearby cities or towns have not been made to conform to the district or sectional standard, and it frequently happens in the event of a large spreading fire that aid is summoned from two or more districts having widely different threads.

For more than half a century the distinct advantages to be derived from the use of uniform fire hose threads has been generally recognized. Valuable outside aid proved of little or no avail in the iloston fire of 1872, the Baltimore conflagration of 1904 and that of Augusta in 1916; a large number of disastrous though smaller fires have occurred at frequent intervals, where non-interchangeable threads contributed to the appalling losses that were sustained.

While the urgent need of uniformity in fire hose threads has been recognized over a long period of years, as indicated by individual and localized efforts in several sections of the country, it is only within comparatively recent years that really definite and lasting progress has been made towards country-wide standardization.

The first organized effort towards the adoption of a universal standard thread, was made by the International Association of Fire Engineers during their annual conventions from 1873 to 1883. This association advocated and adopted several widely different threads as a standard.

It was not until a Committee on Hose Couplings and Hydrant Fittings of the National Fire Protection Association was appointed in 1905, that,the foundation work was permanently commenced. Through the continued efforts of this Committee, the thread known, as the National Standard promptly received unqualified approval and adoption by all the leading organizations concerned with water supplies, fire departments and fire protection. Addresses were delivered at most of the big conventions, pamphlets containingthe specifications and suggestions for adoption were published and distributed, printed records of existing hose threads were issued, nearly a hundred cities and towns became standard either through adoption, replacement or conversion, and the Doctrine of Standardization was pretty thoroughly spread over the entire country.

This standardization movement, originated, promulgated and carefully fostered by this Committee of the National Fire Protection Association, had been put upon a firm foundation, but with the superstructure still to be erected. Up to 1916 a comparatively small percentage of the protected cities and towns in the United States were using the National Standard Thread. It was evident that the desired progress had not been made, due to the absence of co-ordinated effort towards accomplishing in the field the actual work of standardization. Tools had to be perfected and tried out, and a great deal of time necessarily had to be spent on field work, all involving a considerable amount of investigation and expense.

In July. 1917, the work of the Committee of the National Fire Protection Association was, through mutual agreement, taken over by the Committee on Fire Prevention and Engineering Standards of the National Hoard of Fire Underwriters. The world war intervened, and it was not until the spring of 1919 that any very material progress was made by the latter organization.

The Specifications of the National Standard Thread for Fire Hose Couplings and Fittings were determined after careful consideration of the relative preponderance of threads in use as the best intermediary for country-wide adaptability, and were agreed upon in joint conference with accredited representatives of a number of interested organizations.

They have received official approval and adoption by the following organizations:

American Society of Mechanical Engineers,

American Society of Municipal Improvements,

Bureau of Standards—U. S. Department of Commerce,

Fire Marshals’ Association of North America,

International Association of hire Engineers,

Minnesota State Firemen’s Association,

National Board of Fire Underwriters,

New England Water Works Association,

North Carolina State Firemen’s Association,

Pacific Coast Association of F ire Engineers,

Virginia State Firemen’s Association.

The full sized half-tone represented in Figure 1 indicates the specified dimensions with the fullest details needed for the making of the established Standard Thread.

The following tabulation gives the detailed dimensions and specifications for National Standard Threads adopted for all sizes of hose couplings and fittings from 2 1/2 to and including 4 1/2 inches in diameter.

Female end cut 1/8 inch shorter than male for endwise clearance.

Outer ends of Male ayd Female threads terminated by the “Higbee Cut,” to avoid crossing and mutilation of otherwise finely drawn out thread. Outer end of Male thread left bank for 1/4 inch.

The use of more or less 3-inch hose in conjunction with 2 1/2-inch is an established practice in many of our municipal fire departments. To avoid confusion and delays in connecting up, 3-inch hose should be fitted with the National Standard couplings for 2 1/2inch hose. Flow tests indicate that the additional frictional losses, due to the use of the smaller couplings on 3-inch hose, are so small that they may safely be disregarded.

Contracts for all new hose, hydrants or special fire hose fittings should specify that the threads on couplings, nipples, etc., shall be in exact conformity with the National Standard.

The duty of lessening the enormous fire drain upon American efficiency is an obligation of supreme importance in this time of readjustment. Much of this drain has been occasioned by misfits in fire hose threads. The National Standard having received the unqualified approval of all leading interests, its early adoption in all localities becomes a paramount necessity.

STANDARDIZATION OF EXISTING HOSE THREADS.

There are about 8,000 cities or towns in the United States and Canada that have fire hose fiittings in service. Carefully compiled records indicate that approximately 1 per cent, of the total are already using the National Standard thread, 70 per cent, have threads that may readily be resized and made Standard, and the remaining 15 per cent, have either 6 threads to the inch or use one of the various types of snap or clutch couplings.

Recent accomplishments in the field through the use of specially designed and perfected standardization tools have Conclusively shown that this 70 per cent of the existing threads may be made Standard, in a thoroughly satisfactory manner and at a very small cost. Some of the 6-thread fittings may be altered to make a good and serviceable fit with the Standard ; as a general proposition the work of conversion on this type of thread produces unsatisfactory results and complete replacement is considered the best solution.

It is believed that the remedy for this small percentage of non-convertible threads will be found in a universal recognition of the indispensability of the National Standard, and that the immediate problem can safely be confined to the Standardization of the existing threads in this 70 per cent, of the municipalities.

We are indebted to the Greenfield Tap and Die Corporation of Greenfield, Massachusetts, for the design of the thread cutting tools shown, in Fig. 2 and for the following description of their uses.

The numbers used in the following description of the uses of these tools correspond with those indicated in Fig. 2.

No. 1—Roughing Die and Stock,—For use on all male fittings having an outside diameter of thread larger than 3-1/16 inches and up to and including 3-3/32 inches. This die has a wide range of adjustment by means of set screws shown in the stock. The object in the application of this die is to chase down the outer ends of oversized threads to more readily receive cutters on the sizing die (No. 2). This roughing tool should be run onto the oversized fitting as far as possible, in order to distribute the work evenly between the two dies and insure reducing the outer threads sufficient to permit the sizing die to start on easily.

No. 2—Sizing or Finishing Die.—For rethreading oversized male fittings so as to conform with the National Standard. To be used on all sizes larger than 3-1/16 inches only after the application of the roughing die. Can be used alone on sizes 3-1/16 inches and smaller. Should not be used on sizes appreciably smaller than 3-1/16 inches until after the fitting has been expanded.

No. 3—Thread Limit Gage.—Accurately set to the “Pitch Diameter” (2.9670 inches) for gaging National Standard male threads. To be used in gaging threads rechased with the sizing die (No, 2); also in gaging the enlargement of undersized fittings by means of the expander (No. 8) until the maximum ]K>ints on gage just start to bind when passed by the threads of the fitting. This.gage, together with No. 7, should also be used in testing the accuracy of threads on all newly purchased fittings where National Standard threads are specified.

No. 4—Check Block.—For accurately setting Thread Limit Gage No. 3.

No. 5—Roughing Tap.—This is a tapered tool about 3/32 inch under Standard size at the point. For use in roughing out undersized female fittings to enable the finishing tap to enter freely. The Standard diameter is about 3/4 inch back from the point of this tapered tap. In roughing out it should therefore be run in until about 3/16 inch of the cutters remain outside of the fitting, thereby allowing he finishing tap sufficient clearance to get an easy start.

No. 6—Sizing or Finishing Tap.—For rethreading undersized female fittings in conformity with the National Standard. On sizes appreciably smaller than the Standard it should be used only after the Roughing Tap (No. 5) has been first applied. On fittings with either 7or 8-thread pitches and threads equal to or slightly over the Standard pitch diameter, this finishing tap may be used without the rougher, as there would be very little material to be removed.

No. 7—Plug Gage.—Made to conform presisely with the National Standard Female Thread. For use in gaging fittings after they have been cut by the finishing tap (No. 6). Should also be used in conjunction with the Thread Limit Gage (No. 3) in testing threads on all new fittings.

No. 8—Roller Expander.—For use in expanding undersized male fitings, as small as 2-31/32 inches, and if there is a good thickness of metal possibly as small as 2-15/16 inches, up to the Standard pitch diameter. It also can be used to good advantage in repairing jammed or mutilated fitings.

No. 9—Tap wrench.—Two are finished, one for roughing tap No. 5. the other for finshing tap No. 6. Each tap is held firmly in the wrench by means of set-screw shown in cut.

No. 10—Vice with Special Jaws.—For holding hose couplings without undue distortion by means of lugs on couplings inserted in recesses shown in jaws. Though not shown in cut, regular pipe jaws are also furnished for effectively gripping special fittings not provided with the projecting lugs.

No. 11—Special Jaws.—For use in plain bench vice to permit of the simultaneous standardization of male and female hose couplings as indicated in big. 6. These jaws similar to those in No. 10 are recessed to receive the spanner lugs on hose couplings.

No. 12—Suitable Tool Chest (Not illustrated).— For containing the complete set of Standardization Tools described above.

During the latter part of May, 1919, non-standard threads on all hose couplings, hydrant nipples and caps, playpipes and other special fittings and connections to fire apparatus or equipment, in the municipalities and proteced manufacturing plants of High Bridge and Lambertville, N. J., and New Hope, Pa., were resized atid left in exact conformity with the National Standard.

Except for the roughing die, which had not been satisfactorily perfected at the time, the tools used were essentially those shown in Figure 2. This was the first comprehensive trial test of these Standardization tools that had been made in the field.

A total of 191 sets of hose couplings, 84 special fittings, and 219 hydrant outlets were standardized. Including hydrant caps and combination fittings the above represents close to 850 threaded parts, which were resized and made to conform to the National Standard, all with an average of 3 men handling the tools over a period of 7 days’ actual working time. While minor difficulties were experienced due to imperfections in the tools which have since been remedied, the actual work of Standardization was accomplished in a thorough and altogether satisfactory manner.

Following the completion of the above-mentioned field work some little time was devoted to redesigning and adding to the Standardization tools used in the actual field work. The principal perfections made included a redesign of the tapered tap, adding a tapered die, further relieving the taps and dies to facilitate cutting, providing offsets for handles to die stock, and substituting, in the special roller tube expander, 5 rollers in place of 3 to lessen the probability of fracturing undersized male fittings in its use.

In cooperation with the Indiana State hire Marshal, and the Indiana Inspection Bureau, local arrangements were made for demonstrating, with the use of the improved standardization tools, the feasibility of State or country-wide Standardization.

In July, 1919, oversized fittings in Lebanon, Indiana, undersized fittings in Thorntown, Indiana, and a variety of threads in the Indianapolis fire department headquarters were completely standardized.

The results obtained in this second field effort were particularly encouraging and such as to remove beyond a question of doubt that the country-wide standardization of fire hose threads is not only possible but altogether practicable and can be accomplished at a cost to the State or municipality that is almost negligible.

The results obtained in the Indiana towns were as follows:

a.—Lebanon, a town of 8.000 population, had 159 public fire hydrants, 73 sets of hose couplings and various special fittings. The threads originally had an outside diameter of 3-9/128 inches with a pitch of 8 threads to the inch. A total of 496 threaded fittings were made Sandard with an average of 3 men operating the tools in a period of 21 hours actual working time.

b.—The Village of Thorntown had 39 public hydrants, 1,050 feet of 2 1/2-inch fire hose and 3 playpipes, a total of 123 threaded fittings, with threads having an original outside diameter of 3 inches and pitches of 7 1/2 and 8 threads to the inch. The entire work in Thorntown was completed by 4 men operating the tools in 10 hours.

Based upon the rate of progress made on the above field work, it is estimated that 2 experienced men with one complete set of tools can easily standardize all fittings in an average municipality of 5,000 to 10,000 population having about 150 hydrants and say 4,000 feet of fire hose in 3 to 4 days. In a municipality having oversized fittings up to and including 3-3/32 inches outside diameter, am average day’s work should approximate the complete standardization of threads on 75 two-outlet hydrants or on couplings attached to 5,000 feet of hose. Where fittings are undersized down to and including 2-31/32 inches in diameter, some additional time is required : two men should however expand and rechase the threads on close to 200 male fittings in a day. or tap out female fittings of brass at about the same rate: undersized Cast iron hydrant caps can be tapped out and made standard at the rate of 150 to 175 per day.

All manufacturers of hose couplings, hydrant outlets and special fire department hose fittings, should lend the fullest measure of cooperation in this movement for the Standardization of Fire Hose Threads. The existing conditions, with the folly of adhering to the practice of making all sorts and varieties of threads, necessitates frequent alterations and repairs which detract from efficiency and economy on the part of either the manufacturer or the municipality.

Careful calibrations of sample rose couplings obtained from a number of cities that supposedly were equpped with National Standard hose threads, showed that in several instances the variations were such that the threads of one municipality could not be connected up with those of another. Recent measurements made in Newburgh, N. Y., indicated the existence of three distinctly different threads, namely : 2-31/32-inch—7 threads, 3-inch—7 1/2 threads, and 3-1/16-inch—8 threads, all in the one municipality. The practice heretofore common to many of our municipal fire and water departments, that of forwarding sample hose couplings or hydrant nipples to manufacturers in ordering new equipment, has frequently been responsible for the presence of widely differing threads in the equipment of any one city or town. This confusion and delay, due to local misfits, is jointly attributable to carelessness and indifference on the part of the public authorities and the manufacturer.

Each and every manufacturer of threaded fire hose fittings should provide himself with a set of the Standard Thread Gages illustrated by Nos. 3, 4 and 7 in Fig. 2. By so doing he would eliminate any possibility of the slightest variations in turning out the Standard Thread.

The manufacturers are also in a position to materially further this standardization movement, by advising the municipalities in ordering new equipment to purchase the National Standard Thread, with adapters where necessary to serve during the interim required for complete standardization.

SUGGESTIONS FOR THE EARLY CONSUMMATION OF COUNTRY WIDE STANDARDIZATION.

That the State Fire Marshal, in cooperation with municipal fire chiefs in each and every State in the Union, procure the necessary standardization tools, employ an experienced mechanic to accompany each set, subdivide the area of each state into zones of approximately equal work, and with the local assistance that may be readily arranged for in each respective municipality, put into early operation this State-Wide Standardization of Fire Hose Threads.

a.—The State of Indiana has 240 protected cities and towns which to a more or less extent use threaded fire hose fittings. Authentic records indicate that 13 1/2 per cent, of this total are already using the National Standard thread and 70 per cent, have threads that may be readily made Standard. A portion of the fittings in the remaining 16 1/2 per cent, of these municipalities can unquestionably be converted to the Standard, but in the great majority of such cases the best results will be obtained through a complete replacement of the fittings.

b.—It is estimated that 70 per cent, of the Indiana cities and towns can be completely Standardized in 8 months, by keeping in continuous use 6 complete sets of tools, each in charge of an experienced high-grade operating mechanic.

The cost of the entire work is so small, as compared to the advantages to be derived from the elimination of confusion and delays due to the existing misfits, that there is no argument to justify further delay in the early consummation of this most important work of Standardization.

Similar movements toward State-wide Standardization have recently been considered by accredited officials in Kentucky and West Virginia.

Inquiries are now being received from a considerable number of municipalities scattered over the country. indicating a very pronounced determination to effectively remedy, through Country-wide Standardization, tthe long standing evil of Misfits in Fire Hose Threads.

The National Board of Fire Underwriters stand ready at all times to render any State or Municipality every possible assistance in demonstrating the practicability of the Standardization Work in the field and in suggesting the general method of procedure best adapted to obtaining the desired results.